Radiation detectors for the detection of ionizing radiation are widely known. Especially in the field of medical diagnosis, radiation detectors are used which have a high spatial resolution, and to this end are composed of a multiplicity of individual detector elements. These detector elements are usually elements made of scintillator ceramic, which are arranged flat and together provide a multiline detector.
In order to fix the arrangement of the individual detector elements, the matrix of individual detector elements is encapsulated in an encapsulation compound. The purpose of this encapsulation compound is not only to fix the individual detector elements, however, but the encapsulation compound also ensures reflection of the photons produced by the ionizing radiation in the scintillator ceramic. Epoxy resin systems, for example UHU Plus or Araldite, respectively filled with titanium dioxide, are used as the encapsulation compound.
Epoxy resin systems generally consist of two reactive components. On the one hand, they generally include the epoxy resin with the ethylene oxide ring (epoxide group) as a functional group and, on the other hand, they generally include an aminic curing agent whose functional group is aminohydrogen. The reaction of the epoxide group and the curing component takes place in the form of polyaddition. No byproducts are eliminated in this case. In general, stoichiometric crosslinking is achieved when the molar ratio ensures that one epoxide group reacts with one aminohydrogen.
The functionality of the epoxy resin is described by the epoxide equivalent parameter (g/eq), and that of the curing agent is described by the H equivalent index (g/eq). The amount of curing agent which is needed for 100 g of epoxy resin is normally worked out as follows:
                    H        ⁢                                  ⁢        equivalent                    epoxide        ⁢                                  ⁢        equivalent              ×    100    =            mass      ⁢                          ⁢      of      ⁢                          ⁢      curing      ⁢                          ⁢      agent              100      ⁢                          ⁢      g      ⁢                          ⁢      of      ⁢                          ⁢      resin      
The following procedure is to be adopted in order to calculate the mixing ratio of different resins with a curing component:
                              H          ⁢                                          ⁢          equivalent                          epoxide          ⁢                                          ⁢          equivalent          ⁢                                          ⁢          1                    ×              wt        .                                  ⁢        %            ⁢                          ⁢      1        +                            H          ⁢                                          ⁢          equivalent                          epoxide          ⁢                                          ⁢          equivalent          ⁢                                          ⁢          2                    ×              wt        .                                  ⁢        %            ⁢                          ⁢      2        =            mass      ⁢                          ⁢      of      ⁢                          ⁢      curing      ⁢                          ⁢      agent              100      ⁢                          ⁢      g      ⁢                          ⁢      of      ⁢                          ⁢      resin      
The H equivalent of mixtures of different resins can be calculated using the following formula:
            total      ⁢                          ⁢      mass      ⁢                          ⁢      of      ⁢                          ⁢      mixture                                mass          ⁢                                          ⁢          of          ⁢                                          ⁢          curing          ⁢                                          ⁢          agent          ⁢                                          ⁢          1                          H          ⁢                                          ⁢          equivalent          ⁢                                          ⁢          1                    +                        mass          ⁢                                          ⁢          of          ⁢                                          ⁢          curing          ⁢                                          ⁢          agent          ⁢                                          ⁢          2                          H          ⁢                                          ⁢          equivalent          ⁢                                          ⁢          2                    +      …        =      H    ⁢                  ⁢    equivalent    ⁢                  ⁢    of    ⁢                  ⁢    curing    ⁢                  ⁢    agent    ⁢                  ⁢    mixture  
When such known epoxy resin systems are used, the problem arises that the encapsulation compound discolors over time because of the irradiation. The effect of this discoloration is that light produced in the scintillator ceramic is no longer fully reflected, but partly absorbed. The luminous efficiency of a detector element therefore decreases with progressive irradiation. Typical values of the reduction in the luminous efficiency are of the order of 30% after 30 kGy of irradiation.